I had the opportunity to talk to a master Subaru technician about this and they sure do know about it. They still do not seem to know exactly
what causes it but had some good ideas. Even the sales manager said most legacys/outbacks do have this problem to different degrees.
Told me to have the service department make a notice on this at my next service. It sounded like they were waiting for an ECU upgrade for this problem.
They did not know if the '06 would have this solved since they had not seen them yet.

The reason that the WRX STI & the Forester XT doesn't have this problem with their manual transmissions, is that their is no catylitic restriction in up pipe. Our cars have the restriction, unless we replace with an uppie.